Negative Refractive Index Ferromagnetic Materials with Negative Permeability at Zero Applied Magnetic Field

Negative magnetic permeability of ferromagnetic materials is studied in the microwave frequency region. The magnetic permeability is analyzed by employing the dynamic equation of motion of magnetization for different directions of the applied magnetic field with respect to crystalline axes. In the calculations, a very thin ferromagnetic layer with the cubic magneto-crystalline anisotropy energy is considered. It is found that there can be multiple regions of the field value in which the real component of the dynamic permeability becomes negative. In addition, the low-field region for negative permeability can be extended even to the zero external static magnetic field.     

Phase shift analysis of modulated photocurrent: Determination of the energy scale

For the determination of the density of states in the mobility gap of amorphous semiconductors using the phase shift analysis of modulated photocurrent, this paper suggests that making use of the magnitude of the induced photocurrent helps to remove arbitrariness in the energy scale. The working equations for the density of states and the corresponding energy position are expressed in terms of the intensity of the photocurrent. A simulation is made for a specific distribution, to investigate the validity of the procedure. The results show that the profile of the energetic distribution of localized states and the exact energy position of each state are consistent with the original distribution considered.     

Experimental investigation of the humidity induced change in the conduction mechanism of PEG

Characterization of the electrical properties of covalently linked polyethylene glycol thin films under a changing relative humidity is examined by dc measurements. At low humidity levels, electronic conduction takes place while the absorbed water contributes to this mechanism and increases the current. At around 70% relative humidity, as a result of the water clusters formed, the polymer melts from the semicrystalline form and the current shows a steeper increase. The water vapor condenses and conduction takes an ionic nature. There is a hysteresis between the absorption and desorption of water as the film cannot reach its semicrystalline form in the time interval of desorption. The polymer film could attain its pre-absorption form after annealing. PACS 72.60.+g; 72.80.Le     

Low temperature EPR spectra of Fe3+ centers in ternary layered TlGaS2 crystal

The results of low temperature electron paramagnetic resonance (EPR) study of Fe doped TlGaS₂ single crystal in the temperature range of 5‐300 K are presented. Iron was added to the growth mixture in amounts corresponding to a molar ratio Fe/Ga of about 1%. The EPR signal due to Fe³⁺ centers located at the centers of GaS₄ tetrahedrons has been observed. A transformation of EPR spectra has been observed on decreasing the temperature, which is attributed to lowering of the number of resonance lines. The simulation of rotational patterns of the resonance fields exhibits a decrease of the number of centers at low temperatures as a contrary to those of isostructural compounds of TlGaS₂. On comparing the EPR spectra of Fe³⁺ centers in TlGaSe₂, it has been revealed that the Tl atoms lose their zigzag alignment observed previously at room temperature and rearranged to equal structural positions on Tl chains on lowering the temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

New peripherally tetra-[trans-3,7-dimethyl-2,6-octadien-1-ol] substituted metallophthalocyanines: synthesis,characterization and catalytic activity studies on the oxidation of phenolic compounds

In this paper, we elucidated the synthesis, characterization, and investigation of catalytic activity studies of new metallophthalocyanines 4 and 5 as the catalyst for phenolic compounds oxidation by trying different types of oxygen sources. The structural characterization of the products was made by a combination of elemental analysis, FT-IR, LC-MS/MS (for phthalonitrile derivative 3), MALDI-TOF mass spectral data (for metallophthalocyanines 4–7), UV–vis spectroscopy (for metallophthalocyanines 4–7), ¹H NMR and ¹³C NMR spectroscopies (for compounds 3 and 6). The synthetic routes for the (trans-3,7-dimethyl-2,6-octadien-1-ol) substituted phthalonitrile derivative 3 and corresponding metallophthalocyanines 4–7 are outlined in Scheme 1. The MPc complexes 4–7 were synthesized via cyclotetramerization of compound 3 in the presence of the corresponding anhydrous metal salts (CoCl₂ for 4, CuCl₂ for 5, Zn(CH₃COO)₂ for 6 and MnCl₂ for 7) in dry n-pentanol as solvent and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as strong base at reflux temperature under nitrogen gas. Phthalocyanines and their metal complexes, in general, display poor solubility in most of the organic solvents, however, the synthesized metallophthalocyanine complexes 4–7 were highly soluble in common organic solvents because of the introduction of the methyl groups on alkyl chains of peripheral arms. The catalytic activity of compounds 4 and 5 was evaluated for the oxidation of phenolic compounds such as 4-nitrophenol, o-chlorophenol, 2,3-dichlorophenol, and p-methoxyphenol. CoPc 4 displayed good catalytic performance with a full oxidation of 4-nitrophenol into the corresponding benzoquinone and hydroquinone with the highest TON and TOF values within 3 h.     

ESR spectroscopics study of radicals formed from methoxycarbonylcholine picrate hemihydrate

Abstract

The electron spin resonance of γ-irradiated single crystals of methoxycarbonylcholine picrate hemihydrate, C₇H₁₆NO₃ ⁺ · C₆H₂N₃O₇ ^? · ½ H₂O has been observed and analyzed for different orientations of the crystal in the magnetic field. The crystals have been investigated between 70 and 350 K. The spectra were found to be temperature independent and the radiation damage centers are attributed to – ?[Obar]OCH₃ and –CH₂CH₂O? radicals. The g and hyperfine coupling constants were found to be almost isotropic with an average, g = 2.0060, a _H1 = 4.4G for –CH₂CH₂O?, g = 2.0050, a _H2 = 3.5G for –CH₂CH₂O? and g = 2.0045, a _H = 3.5 G for –?[Obar]OCH₃. These values indicate a long-range coupling between the unpaired electron and H protons.